Add support for generating an ignore file.

[btiernay]

First off, great project!

Currently I'm doing something like this in order to generate an ignore file for use with lint and report:

vacuum report ...
jq -r '
  .resultSet.results
  | group_by(.ruleId)
  | map({
      (.[0].ruleId): map("  - " + .path)
    })
  | add
  | to_entries[]
  | "\(.key):\n\(.value | join("\n"))"
' vacuum-report-*  > vacuum.ignore.yaml

It would be nice if that was possible using an existing command.

[lobocv]

I wrote a Go program that does this. I made it into a vacuum CLI command here
#589